The present invention relates to a device and method for removal of rust and paint from a metal surface.
It is estimated that corrosion amounts to 3-4% of the BNP in the western world. Only in Norway millions of square meters are protected by paint each year. In order to achieve good results, the surfaces that are to be painted must be cleaned and pretreated. In industrial applications this is usually done by sandblasting, grinding or jet water washing. Combinations of these methods are also used.
The most frequently used method is sandblasting. Old paint and rust is removed by a blasting the surface with sand or other suitable agents. This is a costly and quite time-consuming process. The advantage of this method is that the blasting process creates a rough surface that gives a good adhesion for new paint. Furthermore, the used equipment is cheap, simple to operate and easy to maintain. The disadvantages with this method is that large quantities of sand are used, which generates a lot of dust, the equipment is heavy and awkward to handle, the method is slow and does not remove grease and other foulings such as water soluble salts, sulfates etc.
Jet water washing is a paint and rust removal method that has become more usual. The advantages of this method are that dust related problems are avoided, there is less waste, and water-soluble foulings are removed. The disadvantages of this method are that the equipment is expensive and difficult to maintain, no roughness is made on the steel surface, a lot of water is spilled, large quantities of water is required (which is a problem on e.g. a ship), and the treated surface must be dried before it can be painted.
Grinding is a method that no longer often is used. The method is mainly used for patchwise repairs.
Most often, the paint is mainly intact on the surface that is to be cleaned. Optimally, the paint only has to be removed, because the roughness on the steel surface is intact. An example is power plants, where the piping is sandblasted even if 95% of the existing paint is intact. The situation is the same in offshore applications.
There are increasing numbers of restrictions on sandblasting and alternative methods have continually been attempted without success.
The present invention aims at avoiding the aforementioned disadvantages, while providing a method and a device that more effectively removes paint and rust.
Further advantages and preferred embodiments are mentioned in the independent claims and in the specification under reference to the enclosed drawing, which shows a preferred embodiment of the present invention.
According to the present invention, rust and old paint is removed by means of induction heat. In addition, grease and other foulings are removed from the surface. This is a quick and reliable method that does not produce excessive waste.
Induction heat is created in magnetic metals by means of magnetic fields. This is a known principle and is used for heating steel in bending and punching processes, and in welding of steel and pipes, e.g. in connection with production of body details in the car industry.
By induction heating the steel to 250-300xc2x0 C., the steel is heated without heating the rust and paint. The steel will expand and attached rust will peel of due to the much lower expansion coefficient of rust as compared to steel. The paint will peel of as a result of the heated surface.